1. Field of the Invention
The present invention relates to a painting apparatus; and more particularly to a painting apparatus having a booth, an air supply system and an exhaust system.
2. Description of the Prior Art
In conventional painting apparatus, which has a booth, and wherein objects are painted while passing through the booth, such as car bodies, for example, the booth is formed along a straight path. Thus, objects to be painted are brought into the booth through an entrance at one end of the booth and conveyed in a straight line through several successive zones in the booth, and then the objects are brouqht out of the booth at an exit located at the end of the booth opposite the entrance. An example of such painting apparatus is described in the July 1984 issue of a publication entitled "PRODUCT FINISHING" which has an exhaust air circulation system similar to that illustrated in FIG. 1. As shown in FIG. 1, booth 1 is constructed to extend along a straight path or line in the conveying direction 2 of the objects being painted. The room or space in the booth is divided into several zones, such as manual painting zones, an automatic painting zone, etc. Generally, in a booth for car bodies, manual painting zones are positioned at the front and rear portions of the booth in the longitudinal direction of the booth, and an automatic painting zone is positioned in an intermediate portion of the booth. In FIG. 1, air conditioner 3 for manual painting zones and air conditioner 4 for automatic painting zone are provided in the front and rear positions of the booth 1. From air conditioners 3 and 4, controlled air is supplied to each zone via ducts, part of the air exhausted from the zones, is circulated to a specific zone (usually an automatic painting zone), and the remainder of the exhausted air is directed to the outside of the system.
In the drying technology following the painting of an object, as shown in FIG. 2, a drying oven 6 having a conveyor line 5, which reverses direction of turning back upon itself is known.
In the above-mentioned straight booth which has manual painting zones in the front and rear portions of the booth, for instance, as shown in FIG. 3, air supply duct 9 extends from air conditioner 3 for manual painting zones 7 and 8. The air supply duct to manual painting zone 8 interferes with air supply duct 11 extending from automatic painting zone air conditioner 4 to automatic painting zone 10. To avoid the interference, air supply duct 9 or 11 must be formed in a complicated shape, thereby decreasing the design freedom and increasing the difficulty in the construction of the duct. Although exhaust ducts are not shown in FIG. 3, there are similar problems with exhaust ducts. To solve the above problems, a separate air conditioner may be provided for the front manual painting zone 7, and the rear manual painting zone 8. However, since the air conditioner itself is large and expensive, it is difficult and impractical to provide an air conditioner for each of the two painting zones. In recent years, robots have been used in automatic painting zones. Usually, the use of robots necessitates increasing the entire length of the booth over that of a conventional booth. Therefore, duct 9 in FIG. 3 tends to become longer, thereby increasing the difficulty and cost in the construction of the duct.
Moreover, there is a basic space problem in construction of the conventional painting apparatus with a straight line booth. The width of the straight line booth for car bodies is about 5 meters, but the width of the air conditioner is, for example, 10-15 meters. Thus, the air conditioner cannot be placed directly on the booth. Typically, as shown in FIG. 3, air conditioners 3 and 4 are installed at positions laterally spaced from the upper portion of booth 12, with only the ducts being positioned above the booth 12. In the arrangement of such a structure, a wide space is required for the entire apparatus.
Additionally, there is a problem with heat energy in the conventional painting apparatus. There are two types of air supply and exhaust systems for a booth. One is a system where exhaust air from one zone of the booth is circulated as supply air to another zone via an air conditioner. Another is a system where exhaust air from a zone of the booth is exhausted to the outside of the booth without circulation to another zone. In any type of such system, since the exhausted air contains solvent, it is necessary to purify finally exhausted air by recovering the solvent contained in the exhausted air with a solvent adsorber. In a conventional system, for example as shown in FIG. 4, the intake air through filter 21 and controlled by air conditioner 22, is forced into painting room 24 by air supply fan 23. The air from the painting room 24 is exhausted to the outside by exhaust fan 25, as purified air, after most of the solvent contained in the exhausted air is recovered by solvent adsorber 26.
In such a system, however, since the air in the painting room 24 picks up a paint mist, a means such as a wet scrubber 27 of FIG. 4 is provided, to catch the paint mist contained in the exhausted air. Thus, air exhausted from the booth is in a state of high humidity. Consequently, in addition to the solvent, a large amount of water is adsorbed by solvent adsorber 26. The solvent adsorption ability of the solvent adsorber 26 thus decreases by the amount of the adsorbed water. As a result, the frequency of regeneration for the solvent adsorber 26 becomes high, and large amounts of heat energy must be consumed for the regeneration.
Furthermore, there is a problem with energy efficiency in a conventional painting apparatus having a flash-off zone in a booth. The flash-off zone is usually provided at a position between a front painting zone and rear painting zone. In the apparatus having such a flash-off zone, the air system (that is, air supply and exhaust system) for the flash-off zone is provided separately from the air systems for the front painting zone and the rear painting zone.
However, since the flash-off zone is a zone for evaporating the solvent contained in the paint film of painted objects; and basically, paint mist does not exist in such a zone, the exhausted air from the flash-off zone can be re-circulated back into the flash-off zone.
Actually, however, such re-circulation has not been achieved for the following reason. Since the flash-off zone is positioned between the front and rear painting zones, and there is more or less of an imbalance between the amount of supply air and the amount of exhaust air in the front painting zone and the rear painting zone, an air flow occurs into or through the flash-off zone. Since paint mist exists in the front and rear painting zones, part of the paint mist flows into the flash-off zone together with the above air flow. Therefore, in order to circulate the air in the flash-off zone, the paint mist contained in the circulating air must be almost completely eliminated by a filter. To eliminate the paint mist having very small particle sizes, a high-efficiency filter is required. However, if such a high-efficiency filter is applied, a clogging of the filter occurs in a short period of time. Thus, the life span of a high-efficiency filter is too short, to be practical for use in the air circulation system of the flash-off zone. As a result, even in the air system for the flash-off zone, the air from the flash-off zone cannot be improved by exhausting it to the outside without re-circulation to the flash-off zone. Therefore, it is difficult to improve the heat efficiency in the conventional air system.